System and Method for Controlling Powder Bed Density for 3D Printing

ABSTRACT

A system and corresponding method for additive manufacturing of a three-dimensional (3D) object to improve packing density of a powder bed used in the manufacturing process. The system and corresponding method enable higher density packing of the powder. Such higher density packing leads to better mechanical interlocking of particles, leading to lower sintering temperatures and reduced deformation of the 3D object during sintering. An embodiment of the system comprises means for adjusting a volume of a powder metered onto a top surface of the powder bed to produce an adjusted metered volume and means for spreading the adjusted metered volume to produce a smooth volume for forming a smooth layer of the powder with controlled packing density across the top surface of the powder bed. The controlled packing density enables uniform shrinkage, without warping, of the 3D object during sintering to produce higher quality 3D printed objects.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/610,461, filed on Dec. 26, 2017. The entire teachings of the aboveapplication are incorporated herein by reference.

BACKGROUND

Binder jetting is an additive manufacturing technique based on the useof an agent, such as a liquid or liquid binder, to join particles of apowder material, also referred to interchangeably herein as powder, toform a three-dimensional (3D) object. In particular, a controlledpattern of the liquid binder may be applied to successive layers of thepowder material in a powder bed such that the layers of the powdermaterial adhere to one another to form the 3D object. Through subsequentprocessing, such as sintering, the 3D object may be formed into afinished object that may be referred to as a finished 3D part.

SUMMARY

According to an example embodiment, a system for additive manufacturingof a three-dimensional (3D) object may comprise: a metering apparatusconfigured to meter powder material to produce a metered volume of thepowder material deposited onto a top surface of a powder bed; a volumeadjustment apparatus configured to adjust the metered volume to producean adjusted metered volume with a controlled height; a spreadingapparatus configured to spread the adjusted metered volume with thecontrolled height to form a smooth layer of the powder material acrossthe top surface of the powder bed; a printing apparatus configured toapply a fluid to at least one region of the smooth layer, the fluidcausing the smooth layer to bind in the at least one region; and acontroller configured to drive the metering apparatus, volume adjustmentapparatus, spreading apparatus, and printing apparatus to producesuccessive smooth layers with the fluid applied to produce the 3Dobject.

The spreading apparatus may be further configured to compact theadjusted metered volume with the controlled height by reducing voidsbetween particles composing the adjusted metered volume to form thesmooth layer with a packing density that may be controlled along an x,y, or z-axis, or a combination thereof

The metering apparatus may be further configured to meter the powdermaterial at a metering rate. The spreading apparatus may be furtherconfigured to traverse the top surface of the powder bed at a traversalrate and the volume of the powder material metered may be a function ofthe metering rate and the traversal rate.

The volume adjustment apparatus may be further configured to maintain acontrolled height for each adjusted metered volume ahead of traversal bythe spreading apparatus along the powder bed, the controlled heightbeing controlled across each respective volume metered to form a givenlayer of the powder bed. To maintain the controlled height, the volumeadjustment apparatus may be further configured to remove an excessamount of the powder material, the excess amount removed being powdermaterial of the volume above a target height.

The volume adjustment apparatus may be located between the spreadingapparatus and the metering apparatus.

The volume adjustment apparatus may be further configured to remove anexcess amount of the powder material, the excess amount removed beingpowder material of the volume above a target height.

The volume adjustment apparatus may be further configured to direct theexcess amount removed to a storage container employed by the meteringapparatus.

The storage container may be a blender. The blender may be configured toblend the excess amount of powder material removed with another amountof the powder material to maintain a proportion of particles of thepowder material removed and previously unpassed through the meteringapparatus.

The volume adjustment apparatus may include a skimming device configuredto skim the volume to remove the excess amount.

The skimming device may include a knife-edge, the knife-edge being asharp, narrow, knife-like edge. The skimming device may be furtherconfigured to contact the volume with the knife-like edge to skim thevolume to remove the excess amount.

The volume adjustment apparatus may include a vacuum device configuredto suction the volume to remove the excess amount and pull the excessamount removed into the vacuum device.

The vacuum device may include a roller with air vents configured tosuction the excess amount.

The volume adjustment apparatus may include a helical shaft. The volumeadjustment apparatus may be further configured to rotate the helicalshaft about an axis of the helical shaft to cause the excess amountremoved to flow, laterally, off the powder bed.

The volume adjustment apparatus may include a compaction rollerconfigured to rotate about an axis of the compaction roller, the axisangled relative to a direction of travel of the compaction roller acrossthe top surface of the powder bed to direct the excess amount removed toflow, laterally, off the top surface of the powder bed.

The volume adjustment apparatus may include a skimming device, a vacuumdevice, or a combination thereof

The volume adjustment apparatus may include a compaction rollerconfigured to pre-spread each volume to produce each adjusted meteredvolume with a controlled height ahead of travel of the spreadingapparatus across the powder bed, the controlled height being controlledacross each respective adjusted metered volume.

The compaction roller may be configured to rotate such that, at acontact point between the compaction roller and the top surface of thepowder bed, a tangential direction of travel of the contact point withthe top surface of the powder bed is in a same direction of travel ofthe spreading apparatus across the powder bed.

The compaction roller may be a first compaction roller, and thespreading apparatus may include a second compaction roller configured tospread the adjusted metered volume.

The second compaction roller may be configured to rotate in a samedirection as the first compaction roller.

The system may further comprise a sensor configured to sense a height ofthe volume. The controller may be further configured to adjust aparameter based on the height sensed. The parameter may be employed bythe volume adjustment apparatus to affect the height of its respectiveadjusted metered volume.

Alternative method embodiments parallel those described above inconnection with the example apparatus embodiment.

According to yet another example embodiment, a system for additivemanufacturing of a three-dimensional (3D) object may comprise: means foradjusting a volume of a powder material metered onto a top surface of apowder bed to produce an adjusted metered volume with a controlledheight; means for spreading the adjusted metered volume with thecontrolled height for forming a smooth layer of the powder materialacross the top surface of the powder bed; means for applying a fluid toat least one region of the smooth layer, the fluid causing the smoothlayer to bind in the at least one region; and means for controlling saidmeans for adjusting, spreading, and applying to produce successivesmooth layers with the fluid applied to produce the 3D object.

It should be understood that example embodiments disclosed herein can beimplemented in the form of a method, apparatus, system, or computerreadable medium with program codes embodied thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments, as illustrated in the accompanyingdrawings in which like reference characters refer to the same partsthroughout the different views. The drawings are not necessarily toscale, emphasis instead being placed upon illustrating embodiments.

FIG. 1A is a block diagram of an example embodiment of a portion of asystem for additive manufacturing of a three-dimensional (3D) object.

FIG. 1B is a block diagram of an example embodiment of a system foradditive manufacturing of a 3D object.

FIG. 2 is a block diagram of an example embodiment of a “skimmer”positioned between a powder metering apparatus and a spreadingapparatus.

FIG. 3 is a block diagram of an example embodiment of a vacuum devicepositioned between a powder metering apparatus and spreading apparatus.

FIG. 4 is a block diagram of an example embodiment of a combination ofexample embodiments of the “skimmer” and vacuum disclosed with referenceto FIG. 2 and FIG. 3, respectively, the combination positioned between apowder metering apparatus and spreading apparatus.

FIG. 5A is a block diagram of an example embodiment of an augerpositioned between a powder metering apparatus and spreading apparatus.

FIG. 5B is a block diagram of an example embodiment of the auger of FIG.5A.

FIG. 6 is a block diagram of an example embodiment of a two-stagecompaction roller.

FIG. 7 is a block diagram of a top-down view of an example embodiment ofa compaction roller angled with respect to a direction of travel.

FIG. 8 is a flow diagram of an example embodiment of a method foradditive manufacturing of a 3D object.

FIG. 9 is a block diagram of an example embodiment of a powder bed.

FIG. 10 is a block diagram of an example embodiment of a spreadingapparatus and tangential direction of travel.

FIG. 11 is a block diagram of an example internal structure of acomputer in which various embodiments of the present disclosure may beimplemented.

DETAILED DESCRIPTION

A description of example embodiments follows.

In a binder jetting process for additive manufacturing, also referred tointerchangeably herein as three-dimensional (3D) printing, a thin layerof powder (e.g., 50 μm) may be spread onto a powder bed that may becomposed of one or more layers of powder or an area for spreading aninitial layer of powder. Spreading of the thin layer of powder may befollowed by deposition of a liquid binder in a two-dimensional (2D)pattern or image that represents a single “slice” of a 3D shaperepresenting a 3D object (also referred to interchangeably herein as a3D part). Following deposition of the liquid binder, another layer ofpowder may be spread, and the process may be repeated to form the 3Dshape composed of bound material, also referred to herein as a boundpart, inside the powder bed. After printing, the bound part may beremoved from the powder bed, leaving behind excess powder that was notbound during the process, and the bound part thereafter is typicallysintered at high temperature. The sintering may be performed to“densify” the bound part to full density (i.e., removal of all voidspace) or may be performed to bind the particles only lightly withoutsubstantial removal of void space.

During spreading of powder, it may be useful to have the powder fill toa high density (tighter packing of the particles) as this translates tolower shrinkage because less void space needs to be removed. Higherdensity packing of the powder may lead to better mechanical interlockingof particles, leading to lower sintering temperatures, and reducedslumping (deformation due to gravity) during sintering. Additionally, itmay be useful to have the powder density be uniform to allow uniformshrinkage of the bound part during sintering, without warping.

During powder spreading, non-uniformity of powder packing density in thepowder bed may result from non-uniform spreading, packing, etc. Duringsubsequent processing (e.g., sintering), variation of packing densitymay translate into differential shrinkage of the 3D part, causingwarping or cracking of parts. As such, uniform and consistent powder bedpacking density may be useful for predicting shrinkage and enablingtight tolerances of final part geometry.

FIG. 1A is a block diagram of an example embodiment of a portion of asystem 100 for additive manufacturing of a three-dimensional (3D)object, such the additive manufacturing system 100 of FIG. 1B, disclosedfurther below with reference to a metal binder jetting printingapplication It should be understood that embodiments disclosed hereinare not limited to a metal binder jetting printing application and mayhave application in other binder jetting applications, such as ceramicbinder jetting and plastic binder jetting applications, laser-basedadditive manufacturing applications, such as direct metal lasersintering (DMLS), or any other additive manufacturing application inwhich powder is spread layer-by-layer.

In the example embodiment of FIG. 1A, a volume adjustment apparatus 110is configured to adjust a volume 115 of a powder material 105 that hasbeen metered onto a top surface 118 of a powder bed 122 to produce anadjusted metered volume 102. The powder material 105 may be referred tointerchangeably herein as powder. Example embodiments for the volumeadjustment apparatus 110 are disclosed further below with reference toFIGS. 2-7.

The powder material 105 is metered by a metering apparatus 120configured to meter the powder material 105 onto the top surface 118 ofthe powder bed 122. The metering apparatus 120 may be any suitablemetering apparatus, such as a hopper, or any other suitable meteringapparatus configured to meter the powder material 105 onto the topsurface 118 of the powder bed 122. The portion of the system 100includes a spreading apparatus, that is, the compaction roller 104, thatis configured to spread the adjusted metered volume 102 to produce asmooth volume 106 for forming a smooth layer 108 of the powder material105 with a controlled packing density and height 112, that may be asubstantially uniform packing density and height across the top surface118 of the powder bed 122. The smooth volume 106 may be considered a“smooth” volume as it may be a smoothed (e.g., leveled, flattened,evened) version of the adjusted metered volume 102. The controlledpacking density and height 112 may be substantially uniform within agiven tolerance, such as ±0.1%, ±0.5%, ±1%, or any other suitabletolerance that may depend on a particular application or parameter. Forexample, the substantially uniform packing density may be considered tobe substantially uniform based on amount of void space of the smoothlayer 108 being within a tolerance, such as, ±0.1%, ±0.5%, ±1%, orwithin any other suitable tolerance, of a void space threshold, the voidspace including voids between particles of the smooth layer 108. Thesubstantially uniform height may be considered to be substantiallyuniform based on a height of the smooth layer 108 being within atolerance, such as, ±0.1%, ±0.5%, ±1%, or within any other suitabletolerance, of a target height for the smooth layer 108 along a length ofthe smooth layer 108.

The spreading apparatus may be any suitable spreading apparatus, such asthe compaction roller 104, that is configured to spread the adjustedmetered volume 102. A layer or volume may be understood to be “smooth”based on having a substantially level top surface. The substantiallylevel top surface may be substantially level within a given tolerance,such as ±0.1%, ±0.5%, ±1%, of a target height or any other suitabletolerance that may depend on a particular application or parameter. Itshould be understood that the substantially uniform packing density andheight may be maintained inter-layer and, optionally, intra-layer.Alternatively, the packing density and height may be non-uniform, butare controlled. For example, the packing density and height may becontrolled in a manner that creates intentional gradients in an x, y, orz direction, or a combination thereof.

One example parameter affecting a packing density of the powder bed 122,that is, packing density of one or more layers composing the powder bed122, is a height of the volume 115 of powder material 105 metered aheadof the spreading apparatus 104 for spreading and, optionally,compacting, the volume 115 to form the smooth layer 108 of the powdermaterial 105. The volume 115 of powder material 105 is metered by themetering apparatus 120 ahead of the volume adjustment apparatus in adirection of travel 125 of the volume adjustment apparatus 110 acrossthe top surface 118 of the powder bed 122. According to exampleembodiments, the height may be controlled by various means a) throughf), disclosed below, and with reference to FIGS. 2-7.

-   -   a) “Skimmer” (also referred to interchangeably herein as a        “snowplow”) for skimming the powder material 105 ahead of a        compaction roller 104 to maintain a controlled height, for        example, a constant (i.e., uniform) height 114, of the volume        115 of powder 105 ahead of the compaction roller in a direction        of travel 125 of the compaction roller 104 across the top        surface 118 of the powder bed 122.    -   b) Vacuum between powder metering and spreading to maintain the        constant height 114 of the volume 115 of powder 105 ahead of the        compaction roller 104 performing the spreading.    -   c) Combination of “skimmer” and vacuum to maintain the constant        height 114 of the volume 115 of powder 105 ahead of the        compaction roller 104.    -   d) Auger between powder metering and spreading to remove excess        powder and maintain the constant height 114 of the volume 115 of        powder 105 ahead of the compaction roller 104 performing the        spreading.    -   e) Two-stage compaction roller configured to pre-spread powder        to maintain the constant height 114 of the volume 115 of powder        105 ahead of the compaction roller 104.    -   f) Angled compaction roller to push excess powder to a side of a        build box and maintain the constant height 114 of the volume 115        of powder 105 ahead of the compaction roller 104.        It should be understood that while example embodiments disclosed        above may refer to the spreading apparatus as the compaction        roller 104, the spreading apparatus may be any suitable        spreading apparatus, as disclosed above. Example embodiments for        controlling a height of the volume 115 of powder to maintain the        controlled height 114 for the volume 115 may be employed by the        additive manufacturing system 100, disclosed below. Further, it        should be understood that the volume 115 may be a “moving”        volume that is moving along the powder bed as powder is being        metered, iteratively, along the bed and, thus, height is being        controlled for a “moving” volume. As such, the controlled height        may be considered as being controlled for a non-stationary        (i.e., moving) volume. Alternatively, a layer of the powder may        be metered, fully, along the powder bed, in which case, the        volume 115 may be a fully metered layer that is a stationary        volume.

FIG. 1B is a block diagram of an example embodiment of the system 100for additive manufacturing of a three-dimensional (3D) object 116. Thesystem 100 comprises a volume adjustment apparatus 110 for adjusting avolume of a powder material metered onto a top surface of a powder bed,such as the volume 115 of FIG. 1A, disclosed above, to produce anadjusted metered volume with a controlled height, such as the adjustedmetered volume 102 of FIG. 1A, disclosed above. Example embodiments formeans for adjusting the volume 115 are disclosed below.

FIG. 2 is a block diagram of an example embodiment of a “skimmer” 210positioned between a powder metering apparatus 220, that is, a hopper inthe example embodiment, and a spreading apparatus, that is, a compactionroller 204 in the example embodiment. The powder metering apparatus 220is configured to meter powder material 205 onto a top surface 218 of apowder bed 222 ahead of a direction of travel 225 of the skimmer 210 andcompaction roller 204 across the top surface 218 of the powder bed 222.The skimmer 210 may be referred to interchangeably herein as a skimmingdevice and removes excess powder 226 from the metered powder volume 215,leaving a smooth, adjusted metered volume 202 with a controlled height,such as a uniform height 214, that can be compressed, uniformly, by thecompaction roller 204. Alternatively, the controlled height may benon-uniform, but controlled. The skimmer 210 may be employed as thevolume adjustment apparatus 110 of FIG. 1A, disclosed above, and FIG.1B, disclosed in further detail below.

A position of the skimmer 210 may be adjusted by a controller, such asthe controller 124 of FIG. 1B, based on feedback, as disclosed furtherbelow.

FIG. 3 is a block diagram of an example embodiment of a vacuum device310 positioned between a powder metering apparatus 320, that is, ahopper in the example embodiment, and a spreading apparatus, that is, acompaction roller 304 in the example embodiment. The powder meteringapparatus 320 is configured to meter powder material 305 onto a topsurface 318 of a powder bed 322 ahead of a direction of travel 325 ofthe vacuum device 310 and compaction roller 304 across the top surface318 of the powder bed 322. The vacuum device 310 removes excess powder326 from the metered powder volume 315, leaving a smooth, adjustedmetered volume of controlled height, such as the adjusted metered volume102 of FIG. 1A, disclosed above, that can be compressed, uniformly ornon-uniformly (but controlled), by the compaction roller 304. The vacuumdevice 310 may be employed as the volume adjustment apparatus 110 of thesystem 100 of FIG. 1A, disclosed above, and FIG. 1B, disclosed infurther detail below.

FIG. 4 is a block diagram of an example embodiment of a combination 410of example embodiments of the skimmer 210 and the vacuum device 310,disclosed above with reference to FIG. 2 and FIG. 3, respectively. Thecombination 410 of the skimmer 210 and vacuum device 310 embodimentsyields extra control over a powder height 414 of the volume of powder415 ahead of a spreading apparatus, that is, the compaction roller 404in the example embodiment, in a direction of travel 425 of thecompaction roller 404 across a top surface 418 of a powder bed 422.

The combination 410 of the skimmer 210 and vacuum device 310 embodimentsmay be employed as the volume adjustment apparatus 110 of the system 100of FIG. 1A, disclosed above, and FIG. 1B, disclosed in further detailbelow. The combination 410 is configured to adjust the volume 415 of thepowder material 405 metered by a powder metering apparatus 420 onto atop surface 418 of a powder bed 422 ahead of a direction of travel 425of the combination 410 across the top surface 418 of the powder bed 422.

While the combination 410 includes a single skimmer 210 disposed betweenmultiple vacuum devices 310, it should be understood that thecombination 410 may include any number of skimmer 210 and vacuum device310 elements arranged in any suitable manner to form the combination 410configured to adjust the volume 415. The combination 410 may bepositioned between a powder metering apparatus 420, that is, a hopper inthe example embodiment, and a spreading apparatus, that is, thecompaction roller 404 in the example embodiment.

FIG. 5A is a block diagram of an example embodiment of an auger 510 thatis positioned between a powder metering apparatus 520, that is, a hopperin the example embodiment, and a spreading apparatus, that is, acompaction roller 504 in the example embodiment. The powder meteringapparatus 520 is configured to meter powder material 505 onto a topsurface 518 of a powder bed 522 ahead of a direction of travel 525 ofthe auger 510 across the top surface 518 of the powder bed 522. Theauger 510 is employed to remove excess powder and maintain the height ofthe volume 515 ahead of the compaction roller 504 in the direction oftravel 525. The auger 510 may be employed as the volume adjustmentapparatus 110 of the system 100 of FIG. 1A, disclosed above, and FIG.1B, disclosed in further detail below. A rotational direction of theauger 510 may be any suitable direction. According to an exampleembodiment, the auger 510 may be screw auger.

FIG. 5B is a block diagram of an example embodiment of the auger 510 ofFIG. 5A, disclosed above. According to the example embodiment, the auger510 has a helical shape.

FIG. 6 is a block diagram of an example embodiment of a two-stagecompaction roller 609. A first stage 610 of the two-stage compactionroller 609 provides some compaction and more uniform height of a powdervolume 615 ahead of a second stage 604 in a direction of travel 625across a top surface 618 of a powder bed 622. The second stage 604provides final compaction of the powder volume 615. The more uniformheight 614 may be more uniform relative to an initial level 613 ofuniformity of height of the powder volume 615 as metered by a meteringapparatus 620. The two-stage compaction roller 609 may be employed asthe volume adjustment apparatus 110 and the spreading apparatus 104 ofthe system 100 of FIG. 1A, disclosed above, and FIG. 1B, disclosed infurther detail below. The two-stage compaction roller 609 may beemployed to adjust the powder volume 615 of powder material 605 meteredonto the top surface 618 of the powder bed 622.

FIG. 7 is a block diagram of a top-down view of an example embodiment ofa compaction roller 709 angled with respect to a direction of travel725, causing excess powder to flow 717 to the side and off of a powderbed 722 of powder 705. The angled compaction roller 709 may be employedas both the volume adjustment apparatus 110 and the spreading apparatus104 of the system 100 of FIG. 1A, disclosed above, and FIG. 1B,disclosed in further detail below. For example, the compaction roller709 may be configured to adjust a volume (not shown) of the powdermaterial 705 metered by a hopper 720 onto the powder bed 722. Thecompaction roller 709 may be configured to rotate and move in thedirection of travel 725 across the powder bed 722 such that thecompaction roller 709 spreads and, optionally, compacts, the adjustedmetered volume to form a smooth layer with a controlled packing densityand height. To compact (e.g., compress, condense, densify, pack down,press down) the adjusted metered volume, the compaction roller 709 maybe configured to exert a force(s) on the adjusted metered volume suchthat the powder is caused to be denser, that is, packed more closely(e.g., tightly) such that the powder is denser relative to not havingthe force(s) exerted.

Turning back to FIG. 1B, in addition to the volume adjustment apparatus110, disclosed above, the system 100 further comprises a build area 118,also referred to interchangeably herein as a top surface 118 of a powderbed 122, controller 124, metering apparatus 120 (also referred tointerchangeably herein as a powder dispensing apparatus, meteringapparatus, or powder metering apparatus), spreading apparatus 104, and aprinthead 127. It should be understood that the printhead 127 may becomposed of multiple printheads. The system 100 may include a build box123 for housing the powder bed 122. The powder bed 122 may be supportedby a piston 107, or any other suitable supporting structure for thepowder bed 122 and configured to move down within the build box 123 suchthat subsequent layers of the powder bed 122 may be formed. It should beunderstood that a top surface of the piston 107 or other suitablesupporting structure serves as the top surface 118 of the powder bed,initially, and that each layer of powder formed thereafter serves as thetop surface 118 of the powder bed 122.

According to an example embodiment, the metering apparatus 120 may beconfigured to meter powder material 105 by metering the powder material105 to produce powder flow 103 with a controlled flow rate. The powdermaterial 105 may be referred to interchangeably herein as buildmaterial, feedstock, or simply, powder. The powder material 105 may beintroduced into the metering apparatus 120 in any suitable manner. Themetering apparatus 120 may be a hopper and the powder material 105 maybe a metallic powder. For example, according to an example embodiment,the metering apparatus 120 may be configured to meter metal injectionmolding (MIM) metal powder into a volume with a height, for example, assmall as 30 microns, onto the top surface 118 of the powder bed 122. Themetering apparatus 120 may meter the powder material 105 at a meteringrate. The spreading apparatus 104 may traverse the top surface 118 ofthe powder bed 122 at a traversal rate. The volume 115 of the powdermaterial 105 may be a function of the metering rate and the traversalrate. For example, the volume 115 of the powder material 105 metered maybe a function of a difference between the metering rate and thetraversal rate.

The volume 115 may be adjusted by the volume adjustment apparatus 110and may be spread and, optionally, compacted by the spreading apparatus104 for an even distribution, that is, a substantially uniform height(also referred to interchangeably herein as thickness) and substantiallyuniform packing density, to form a smooth layer of the metal powder. Thevolume adjustment apparatus 110 may be configured to maintain a constantheight of the volume 115 of powder material 105 to form an adjustedmetered volume 102 with a controlled height ahead of the spreadingapparatus 104 that may spread the adjusted metered volume 102 of powdermaterial 105. The spreading apparatus 104 may be further configured tospread, and optionally, compact the adjusted metered volume 102 to formthe smooth layer 108 with a packing density that may be controlled indirections along an x, y, or z-axis, or a combination thereof. Thepacking density may be controlled to be substantially uniform ornon-uniform, but controlled, along the x, y, or z-axis, or combinationthereof. According to an example embodiment, the packing density of thesmooth layer, such as the smooth layer 108 of FIG. 1A, disclosed above,may be controlled by adjusting a height of volume of powder materialbeing spread by the spreading apparatus 104, such as the height 114 ofFIG. 1A.

The volume adjustment apparatus 110 may be located between the spreadingapparatus 104 and the metering apparatus 120. To maintain the controlledheight at a target height, the volume adjustment apparatus 110 may beconfigured to remove an excess amount of the powder material 105, theexcess amount being powder material 105 of the volume 115 that is abovethe target height, such as the excess powder 126 above the target height138 of FIG. 1A.

According to an example embodiment, the excess amount that is removedmay be directed to a storage container (not shown) that stores powdermaterial 105 for delivery to the metering apparatus 120. According to anexample embodiment, the storage container may be a blender configured toblend the excess amount of powder material with another amount of thepowder material 105 to maintain a proportion of the particles removedand previously unpassed through the metering apparatus.

According to an example embodiment, the volume adjustment apparatus 110may include a skimming device, such as the skimmer 210, disclosed abovewith reference to FIG. 2, and may remove the excess amount by skimmingthe volume 115. Skimming the volume 115 may include contacting thevolume 115 with the skimming device, alternatively skimming the volume115 may not include contacting the volume 115 with the skimming device.Skimming may be any suitable action that causes the excess amount to beremoved from the volume 115, the excess amount being above a controlledheight. The skimming device may include a knife-edge, the knife-edgebeing a sharp, narrow, edge that is a knife-like edge. Such a knife-edgemay be referred to as a type of doctor blade by those skilled in theart. Skimming the volume may employ the knife-edge to remove the excessamount. The knife-edge may have an edge thickness that is a function ofa size of a particle of the powder and may be configured to have theedge thickness be less than the size of the particle. According toanother example embodiment, the edge thickness may be a function oftotal size of a given number of particles or a function of a targetthickness of a spread layer. For example, the knife-edge may have anedge thickness that is 1%, 5%, 10%, or any other suitable percentage ofthe target thickness of the spread layer. The knife-edge may be a rigidedge that shows no sign of flex and is stiff in response to contact withpowder and exhibits no measurable motion or bending as it skims thespread layer.

According to an example embodiment, the volume adjustment apparatus 110may include a vacuum device, such as the vacuum device 310 disclosedabove with reference to FIG. 3, and may remove the excess amount bysuctioning the volume 115 with the vacuum device 310 and pulling theexcess amount into the vacuum device 310. According to an exampleembodiment, the vacuum device 310 may include a roller with air ventsconfigured to suction the excess amount.

According to an example embodiment, the volume adjustment apparatus 110may include a combination of a skimming device and vacuum device, suchas the combination 410 of the “skimmer” 210 and vacuum device 310disclosed above with reference to FIG. 4.

According to an example embodiment, the volume adjustment apparatus 110may include a helical shaft, such as the helical shaft of the screwauger 510 disclosed above with reference to FIG. 5B. Removing the excessamount may include rotating the helical shaft about an axis of thehelical shaft causing the excess amount to flow off the top surface 118of the powder bed 122. According to an example embodiment, the excessamount may be caused to flow, laterally, off the top surface 118. Thesystem 100 may comprise a reservoir (not shown) coupled to the powderbed 122 and configured to collect the excess amount.

According to an example embodiment, a two-stage compaction roller may beemployed as both the volume adjustment apparatus 110 and the spreadingapparatus 104, such as the two-stage compaction roller 609 disclosedabove with reference to FIG. 6. Turning back to FIG. 6, a first stage610 of the two-stage compaction roller 609 may be a first compactionroller that pre-conditions the volume 615 by providing some compactionand a controlled height, such as a more uniform height of the volumemetered by the metering apparatus 620 to form an adjusted metered powdervolume ahead of a second stage 604, such as the adjusted metered volume102 of FIG. 1A, disclosed above. The controlled height may be moreuniform relative to a level of uniformity of an initial height 613 ofthe powder volume 615 as metered. Alternatively, the controlled heightmay be non-uniform, but controlled.

The second stage 604 may be a second compaction roller that providesfinal compaction of the metered powder volume by spreading the adjustedmetered volume. Both the first and second compaction rollers may beconfigured to rotate such that, at respective contact points between thefirst compaction roller and the second compaction roller and the topsurface 618 of the powder bed 622, a tangential direction of travel ofthe contact points with the top surface 618 of the powder bed 622 is ina same direction as traversal of the first and second compaction rollersacross the powder bed 622. The tangential direction of travel isdisclosed further below with reference to FIG. 10.

As such, adjusting the volume 615 of powder material 605 may beperformed by a first compaction roller 610 and may include pre-spreadingthe volume to produce the adjusted metered volume with a controlledheight ahead of traversal of a second compaction roller 604 employed asthe spreading apparatus, the controlled height being controlled for theadjusted metered volume. The controlled height may be controlled alongthe adjusted metered volume, such as in a direction of traversal of thespreading apparatus. Alternatively, the controlled height may becontrolled perpendicular or any other suitable angle relative to thedirection of spreading. According to an example embodiment, a height ofthe volume of powder metered 605 may be sensed 636 and an offset inheight of the first compaction roller 610 may be adjusted in response tothe height sensed. Sensing of the height may be performed by a heightsensor (not shown). Alternatively, the height may be sensed by sensing acompaction force applied to the adjusted metered volume by the spreadingapparatus, such as the second compaction roller 604, or by sensing aadjusting force being applied by the volume adjustment apparatus, suchas the first compaction roller 610, to the volume 615 of metered powdermaterial 605. Such sensing of the height may be communicated to acontroller, such as the controller 124 of FIG. 1B, and may serve asadjustment feedback 144 or spreading feedback 146 employed by thecontroller 124 to control the volume adjustment apparatus 110, spreadingapparatus 104, and metering apparatus 120, via adjustment control(s)148, spreading control(s) 150, and metering control(s) 152,respectively.

Turning back to FIG. 1B, according to an example embodiment, the volumeadjustment apparatus 110 may be a compaction roller configured to rotateabout an axis of the compaction roller. The axis may be angled relativeto a direction of the traversal (i.e., travel) of the compaction rolleracross the top surface of the powder bed, such as disclosed above withreference to FIG. 7. Such a compaction roller may be referred to as anangled compaction roller and may direct the excess amount to flow offthe top surface 118 of the powder bed 122. According to an exampleembodiment the excess amount may be direct to flow, laterally, of thetope surface 118. The angled compaction roller may be configured torotate such that, at a contact point between the angled compactionroller and the top surface of the powder bed, a tangential direction oftravel of the contact point with the top surface 118 of the powder bed122 is in a same direction as traversal of the spreading apparatus 104across the powder bed 122, as disclosed further below with reference toFIG. 10.

According to an example embodiment, the spreading apparatus 104 mayinclude a compaction roller configured to compact the adjusted meteredvolume, such as any of the compaction rollers disclosed above withreference to FIGS. 2-5 and 7, and the second compaction roller disclosedabove with reference to FIG. 6. Such compaction rollers may beconfigured to rotate such that, at a contact point between thecompaction roller and the top surface 118 of the powder bed 122, atangential direction of travel of the contact point with the top surface118 of the powder bed 122 is in a same direction as traversal of thespreading apparatus 104 across the powder bed 122, as disclosed furtherbelow with reference to FIG. 10.

The controller 124 may be configured to control the metering apparatus120, volume adjustment apparatus 110, spreading apparatus 104, and theprinthead 127. For example, the controller 124 may be configured tocontrol a metering rate of the metering apparatus 120, motion of themetering apparatus 120 across the powder bed 122, motion of thespreading apparatus 104, motion of the printhead 127, release of thefluid 119 from the printhead 127, and a vertical movement of the topsurface 118 of the powder bed 122. The controller 124 may be furtherconfigured to actuate the printhead 127 to deliver the fluid 119 fromthe printhead 127 to each smooth layer of the powder 122 in a controlledtwo-dimensional pattern as the printhead 127 moves across the topsurface 118 of the powder bed 122. Further, the controller 124 may beconfigured to control position of the metering apparatus 120, volumeadjustment apparatus 110, spreading apparatus 104, and printhead 127relative to the top surface 118 of the powder bed 122 as well asrespective offsets between respective axes of the metering apparatus120, volume adjustment apparatus 110, spreading apparatus 104, andprinthead 127.

The printhead 127 may employ a plurality of jets to selectively depositdroplets of a fluid 119 to bind a smooth layer of metal powder. Suchdroplets of the fluid 119 may be small, for example, two trillionths ofa liter (smallest droplet), and tens of millions of droplets may bedeposited per second, binding the smooth layer of the metal powder.

The printhead 127 may be configured to apply the fluid 119 to at leastone region of the smooth layer. The printhead 127 may include adischarge orifice and, in certain implementations, may be actuated(e.g., through delivery of an electric current to a piezoelectricelement in mechanical communication with the fluid) to meter the fluid119 through the discharge orifice to the smooth layer. The fluid 119 maybe configured to cause the layer to bind in the at least one region toform a bonded layer of the 3D object 116. Heat may be applied to furtherspeed up the binding process and sinter the 3D object 116 to form afinal version of the 3D object 116.

It should be appreciated that the movement of the printhead 127 and theactuation of the printhead 127 to deliver the binder 119 may be done incoordination with movement of the spreading apparatus 104 across the topsurface 118 of the powder bed 122. For example, the spreading apparatus104 may spread and compact a layer of the powder 105 across the topsurface 118 of the powder bed 122, and the printhead 127 may deliver thefluid 119 in a controlled two-dimensional pattern to the smooth layer ofthe powder spread across the top surface 118 of the powder bed 122 toform a bound layer of the 3D object 116. Such operations may be repeated(e.g., with a controlled two-dimensional pattern for each respectivelayer) in sequence to form subsequent layers until, ultimately, the 3Dobject 116 is formed in the powder bed 122, such as the powder bed 922of FIG. 9, disclosed further below.

According to an example embodiment, the metering apparatus 120, volumeadjustment apparatus 110, and spreading apparatus 104 may be configuredto move across the top surface 118 of the powder bed 122 as a unit. Thespreading apparatus 104 may be configured to traverse the top surface118 of the powder bed 122 in a traversal direction. The unit may beconfigured to traverse the top surface 118 of the powder bed 122 in thetraversal direction and meter and adjust volumes of the powder material105 onto the top surface 118 of the powder bed 122 ahead of a traversalby the spreading apparatus 104. The unit may include the printhead 127and the printhead 127 may be configured to apply the fluid 119 followingthe traversal by the spreading apparatus 104 that itself followstraversal by the volume adjustment apparatus 110.

According to an example embodiment, the spreading apparatus 104 and theprinthead 119 may be configured to traverse the top surface 118 of thepowder bed 122 as a unit. The unit may follow traversal by the volumeadjustment apparatus 110. The printhead 127 may be configured to applythe fluid 119 following the traversal by the spreading apparatus 104.

FIG. 8 is a flow diagram 800 of an example embodiment of a method foradditive manufacturing of a three-dimensional (3D) object. The methodbegins (802) and adjusts a volume of a powder material metered onto atop surface of a powder bed to produce an adjusted metered volume with acontrolled height (804). The method spreads the adjusted metered volumewith the controlled height to produce a smooth volume for forming asmooth layer of the powder material across the top surface of the powderbed (806). The method applies a fluid to at least one region of thesmooth layer, the fluid causing the smooth layer to bind in the at leastone region (808). The method controls the adjusting, spreading, andapplying operations to produce successive smooth layers with the fluidapplied to produce the 3D object (810), and the method thereafter ends(812), in the example embodiment.

According to an example embodiment, the meter, adjust, spread, and applyoperations may be operations that are activated, sequentially. Accordingto another example embodiment, at least two of the meter, adjust,spread, and apply operations may be operations that are activated,concurrently.

It should be understood that a direction of travel for the meter,adjust, spread, or apply operations may be in any suitable directionrelative to the top surface of the powder bed. Further, such directionmay be a uni- or bi-directional. Further, it should be understood thatthe control of such operations may be performed by a controller, such asthe controller 124 of FIG. 1B, disclosed above. The controller may be aprocessor, such as the central processing unit 1118 of FIG. 11,disclosed further below, digital signal processor (DSP), fieldprogrammable gate array (FPGA), proportional-integral-derivative (PID)controller, or any other digital or analog controller, combinationthereof, or equivalent thereof.

It should be understood that the controller 124 may control the meter,adjust, spread, and apply operations such that the operations areperformed in an iterative manner. However, such iterations may includeperforming multiple repetitions of any one operation prior to performinganother such that there is not a 1:1 correspondence. For example, thecontroller 124 may control the operations such as: meter, adjust,spread, apply. Alternatively, the controller may control the operationssuch as: meter . . . meter, adjust . . . adjust, etc. It should beunderstood that the controller may control the meter, adjust, spread,apply operations in any suitable manner.

According to an example embodiment, the controller 124 may be configuredto receive feedback that may include sensor information, such as sensedheight of the volume metered, sensed height of the adjusted meteredvolume, or any other suitable sensor information, such as packingdensity of the smooth volume, collection rate of excess powder removed,adjustment feedback 144 from the volume adjustment apparatus 110,spreading feedback 146 from the spreading apparatus, or a combinationthereof. Such feedback may be employed by the controller 124 to performclosed loop control over the meter, adjust, spread, and applyoperations.

For example, sensed information regarding height of the volume of powdermetered, height of the adjusted metered volume, etc. may be used by thecontroller 124 to adjust parameters of the metering apparatus 120,volume adjustment apparatus 110, spreading apparatus 104, or acombination thereof. The parameters adjusted may include position of thevolume adjustment apparatus 110 relative to the spreading apparatus 104,rate of traversal, rate of metering, or any other suitable parameter orcombination of parameters. Sensing the height may include obtaining theheight from a sensor device (not shown). Alternatively, the height maybe sensed based on feedback regarding torque, drive current, rotationalspeed, etc. of the volume adjustment apparatus 110 or the spreadingapparatus 104.

The spreading feedback 146 may include information regarding rotationalspeed, acceleration, velocity, torque, forces in directions parallel tothe spreading direction and normal to the powder layers, an amount ofelectrical current being employed to drive rotation of the spreadingapparatus 104 and to drive translation of the spreading apparatus 104,or any other suitable information of the spreading apparatus 104. Thespreading feedback 146 may be used by the controller 124 to adjust aparameter of the metering apparatus 120, volume adjustment apparatus110, spreading apparatus 104, or a combination thereof. The parameteradjusted may include an offset in height or other position of the volumeadjustment apparatus 110 relative to the spreading apparatus 104 or thetop surface 118 of the powder bed 122, or any other suitable parameter,such as an air flow velocity being employed by a vacuum device, such asthe vacuum device 310 of FIG. 3, disclosed above, that may be used foradjusting the volume 115.

According to an example embodiment, the spreading feedback 146 may beemployed by the controller 124 to determine a level (i.e., degree) ofuniformity of the smooth volume 106 and may be configured to adjust themetering apparatus 120, volume adjustment apparatus 110, the spreadingapparatus 104, or a combination thereof based on the level of uniformitydetermined. For example, the controller 124 may adjust height, speed ofrotation, traversal rate, etc. of either or both of the volumeadjustment apparatus 110 or spreading apparatus 104.

FIG. 9 is a block diagram of an example embodiment of a powder bed 922.According to the example embodiment, the powder bed 922 may be supportedby a piston 907 and surrounded by walls of a build box 923 and thepiston 907 may be configured to move downward following application ofthe fluid 919 by the printhead 927. The build box 923 may comprise aheater 928. The heater 928 may be configured to heat the powder bed 922to dry the fluid 919 and to maintain flowability of the powder material905. The heater 928 may be any suitable heater, such as a resistanceheater embedded in one or more walls of the build box 923 defining thepowder bed 922 or additionally, or alternatively, the heater 928 may bean induction heater. The heater 928 may be controlled (e.g., throughelectrical communication with the controller 924) to heat thethree-dimensional object 916 in the powder bed 922 to a targettemperature.

As disclosed above, operations may be repeated (e.g., with a controlledtwo-dimensional pattern for each respective layer) in sequence to formsubsequent layers until, ultimately, the 3D object 916 may be formed inthe powder bed 922.

FIG. 10 is a block diagram of an example embodiment of a spreadingapparatus and a tangential direction of travel 1032. In the exampleembodiment, the spreading apparatus is a roller 1004 configured totraverse the top surface 1018 of the powder bed 1022 of powder material1005 and rotate such that, at a contact point 1034 between the roller1004 and the top surface 1018 of the powder bed 1022, a tangentialdirection of travel 1032 of the contact point 1034 with the top surface1018 of the powder bed 1022 is in a same direction as traversal of theroller, that is, the direction of spreading 1025 of the roller 1004. Assuch, the roller 1004 may be understood as rolling in reverse of adirection of traversal or a direction of spreading 1025 the powdermaterial 1005 across the top surface 1018 of the powder bed 1022 and maybe referred to as a “counter-rotating” roller.

FIG. 11 is a block diagram of an example of the internal structure of acomputer 1100 in which various embodiments of the present disclosure maybe implemented. The computer 1100 contains a system bus 1102, where abus is a set of hardware lines used for data transfer among thecomponents of a computer or processing system. The system bus 1102 isessentially a shared conduit that connects different elements of acomputer system (e.g., processor, disk storage, memory, input/outputports, network ports, etc.) that enables the transfer of informationbetween the elements. Coupled to the system bus 1102 is an I/O deviceinterface 1104 for connecting various input and output devices (e.g.,keyboard, mouse, displays, printers, speakers, etc.) to the computer1100. A network interface 1106 allows the computer 1100 to connect tovarious other devices attached to a network. Memory 1108 providesvolatile storage for computer software instructions 1110 and data 1112that may be used to implement embodiments of the present disclosure.Disk storage 1114 provides non-volatile storage for computer softwareinstructions 1110 and data 1112 that may be used to implementembodiments of the present disclosure. A central processor unit 1118 isalso coupled to the system bus 1102 and provides for the execution ofcomputer instructions.

Further example embodiments disclosed herein may be configured using acomputer program product; for example, controls may be programmed insoftware for implementing example embodiments. Further exampleembodiments may include a non-transitory computer-readable mediumcontaining instructions that may be executed by a processor, and, whenloaded and executed, cause the processor to complete methods describedherein. It should be understood that elements of the block and flowdiagrams may be implemented in software or hardware, such as via one ormore arrangements of circuitry of FIG. 11, disclosed above, orequivalents thereof, firmware, a combination thereof, or other similarimplementation determined in the future. In addition, the elements ofthe block and flow diagrams described herein may be combined or dividedin any manner in software, hardware, or firmware. If implemented insoftware, the software may be written in any language that can supportthe example embodiments disclosed herein. The software may be stored inany form of computer readable medium, such as random-access memory(RAM), read only memory (ROM), compact disk read-only memory (CD-ROM),and so forth. In operation, a general purpose or application-specificprocessor or processing core loads and executes software in a mannerwell understood in the art. It should be understood further that theblock and flow diagrams may include more or fewer elements, be arrangedor oriented differently, or be represented differently. It should beunderstood that implementation may dictate the block, flow, and/ornetwork diagrams and the number of block and flow diagrams illustratingthe execution of embodiments disclosed herein. Further, exampleembodiments and elements thereof may be combined in a manner notexplicitly disclosed herein.

While example embodiments have been particularly shown and described, itwill be understood by those skilled in the art that various changes inform and details may be made therein without departing from the scope ofthe embodiments encompassed by the appended claims.

1-30. (canceled)
 31. A binder jet system for additive manufacturing of athree-dimensional object, the system comprising: a hopper configured todeposit an amount of powder material onto a powder print bed; anadjustment apparatus configured to adjust a height of the amount ofpowder material on the powder print bed; a spreading apparatusconfigured to spread the amount of powder material across the powderprint bed to form a layer; and a print head configured to deposit afluid to bind at least one region of the layer of powder material. 32.The system of claim 31, wherein the adjustment apparatus is configuredto remove at least a portion of the amount of powder material from thepowder print bed.
 33. The system of claim 32, wherein an intended heightof the powder material is predetermined and the adjustment apparatus isconfigured to remove at least a portion of the amount of powder materialthat causes the amount of powder material to exceed the predeterminedheight.
 34. The system of claim 31, wherein the adjustment apparatus ispositioned between the hopper and the spreading apparatus.
 35. Thesystem of claim 31, wherein the adjustment apparatus is configured toremove at least a portion of the amount of powder material that exceedsa target height from the powder print bed.
 36. The system of claim 35,wherein the adjustment apparatus is further configured to direct atleast a portion of the removed powder material into a container separatefrom the powder print bed.
 37. The system of claim 36, wherein thecontainer is operably coupled to the hopper.
 38. The system of claim 36,wherein the powder material is a metal powder material, and wherein thecontainer is a blender configured to blend the removed metal powdermaterial with another amount of metal powder material.
 39. The system ofclaim 32, wherein the adjustment apparatus comprises a skimming deviceconfigured to skim the amount of powder material to remove at least aportion of the powder material from the powder print bed.
 40. The systemof claim 39, wherein the skimming device includes a narrowed edgeportion that is oriented to contact the amount of powder material toremove the at least a portion of the powder material that exceeds atarget height from the powder print bed.
 41. The system of claim 35,wherein the adjustment apparatus comprises a roller configured to rotateabout an axis.
 42. The system of claim 41, wherein the roller isconfigured to rotate about the axis in a direction such that a portionof the roller closest to the powder print bed rotates in a directionopposite to a direction of travel of the roller.
 43. The system of claim41, wherein the axis of the roller is angled at a non-perpendicularangle relative to a direction of travel of the roller across the powderprint bed.
 44. The system of claim 35, wherein the adjustment apparatusincludes a vacuum device configured to apply suction to the amount ofpowder material to remove the at least a portion of the powder material.45. The system of claim 44, wherein the vacuum device comprises a rollerwith one or more vents configured to apply the suction to the amount ofpowder material to remove the at least a portion of the powder materialthrough the one or more vents.
 46. The system of claim 31, furthercomprising a roller positioned ahead of the spreading apparatus relativeto a direction of travel of the spreading apparatus across the powderprint bed.
 47. The system of claim 46, wherein the roller positionedahead of the spreading apparatus is configured to traverse the powderprint bed in the direction of travel of the spreading apparatus, andwherein the roller is configured to rotate around an axis in a directionsuch that a portion of the roller closest to the powder print bedrotates in a direction opposite to the direction of travel.
 48. A binder^(.)et system for additive manufacturing of a three-dimensional object,the system comprising: a hopper configured to deposit an amount ofpowder material onto a powder print bed; a skimming device configured totraverse the amount of powder material to remove excess powder materialfrom the powder print bed; a spreading apparatus configured to spreadthe powder material to form a layer of the powder material across thepowder print bed; a printing apparatus configured to deposit a fluid toat least one region of the layer to bind the powder material in the atleast one region of the layer; and a controller configured to controlone or more of the hopper, the skimming device, the spreading apparatus,or the printing apparatus.
 49. The system of claim 48, wherein theskimming device includes a narrowed edge portion positioned to contactthe amount of powder material as the skimming device traverses thepowder print bed to remove at least a portion of the excess powdermaterial to adjust a height of the amount of powder material on thepowder print bed.
 50. The system of claim 48, wherein the skimmingdevice is positioned between the hopper and the spreading apparatusrelative to a direction of travel across the powder print bed.
 51. Thesystem of claim 48, further comprising at least one vacuum deviceconfigured to apply suction to the amount of powder material to removethe excess powder material.
 52. The system of claim 51, wherein the atleast one vacuum device comprises a first vacuum device and a secondvacuum device, wherein the first vacuum device is positioned upstream ofthe skimming device relative to a direction of travel across the powderprint bed, and wherein the second vacuum device is positioned downstreamof the skimming device relative to the direction of travel across thepowder print bed.
 53. The system of claim 48, wherein the powdermaterial is a metal powder material, wherein the skimming device isfurther configured to direct the excess metal powder material into acontainer that is operably coupled to the hopper, and wherein thecontainer is configured to blend the excess metal powder materialremoved from the powder print bed with another amount of metal powdermaterial.
 54. A binder ^(.)et system for additive manufacturing of athree-dimensional object, the system comprising: a hopper configured todeposit metal powder material onto a powder print bed; a rollerpositioned downstream of the hopper relative to a direction of travel ofthe hopper across the powder print bed, wherein an axis of rotation ofthe roller is angled at a non-perpendicular angle relative to thedirection of travel; and a print head configured to deposit a fluid toat least one region of the metal powder material to bind the metalpowder material in the at least one region.
 55. The system of claim 54,wherein the roller is configured to at least one of spread or compactthe metal powder material as the roller traverses the powder print bed.56. The system of claim 54, wherein the non-perpendicular angle of theroller is configured to direct at least a portion of the metal powdermaterial off the powder print bed.
 57. The system of claim 56, whereinby directing the at least a portion of the metal powder material off thepowder print bed, the roller reduces a height of the metal powdermaterial on the powder print bed.
 58. The system of claim 56, furthercomprising a container, wherein the roller is further configured todirect the at least a portion of the metal powder material into thecontainer.
 59. The system of claim 58, wherein the container is operablycoupled to the hopper, and wherein the container is configured to blendthe at least a portion of the metal powder material with another amountof metal powder material.
 60. The system of claim 54, wherein the rolleris configured to rotate about the axis of rotation in a direction suchthat a portion of the roller closest to the powder print bed rotates ina direction opposite to the direction of travel of the roller.